Stainless iron-base alloy and its various applications

ABSTRACT

IRON-BASE ALLOY FOR MAKING HIGH-TEMPERATURE WORKING SLUGS, CONTAINING CARBON, NICKEL, CHROMIUM, MANGANESE, SILICON AND THE USUAL IMPURITIES AND HAVING A NIOBIUM CONTENT COMPRISED BETWEEN 0.3 AND 2.0% BY WEIGHT, SAID ALLOY HAVING PREFERABLY THE FOLLOWING COMPOSITION: CARBON-FROM ABOUT 0.05% TO 0.70% BY WEIGHT CHROMIUM-FROM ABOUT 20% TO 30% BY WEIGHT NICKEL-FROM ABOUT 30% TO 40% BY WEIGHT NIOBIUM-FROM ABOUT 0.20% TO 3% BY WEIGHT SILICON-FROM ABOUT 0.50% TO 2.50% BY WEIGHT MANGANESE-FROM ABOUT 0.50% TO 2.50% BY WEIGHT NITROGEN-FROM ABOUT 0.02% TO 0.20% BY WEIGHT PHOSPHORUS AND SULPHUR-LESS THAN 0.05% BY WEIGHT THE TEST BEING IRON.

United Stt atent Patented Dec. 14, 1971 U.S. Cl. 75-128 G 2 ClaimsABSTRACT OF THE DISCLOSURE Iron-base alloy for making high-temperatureworking slugs, containing carbon, nickel, chromium, manganese, siliconand the usual impurities and having a niobium content comprised between0.3 and 2.0% by weight, said alloy having preferably the followingcomposition:

Carbon-frorn about 0.05% to 0.70% by weight Chromiumfrom about to byweight Nickelfrom about 30% to 40% by weight Niobium-from about 0.20% to3% by weight Siliconfrom about 0.50% to 2.50% by weight Manganesefromabout 0.50% to 2.50% by weight Nitrogenfrom about 0.02% to 0.20% byweight Phosphorus and sulphurless than 0.05% by weight the rest beingiron.

The present invention essentially relates to iron-base alloys of thetype adapted for producing high-temperature operating slugs andexhibiting high mechanical strength, low creep, good resistance tocorrosion and to thermal shocks in temperature ranges from about 800 C.to 1250 C., and principally capable of being very readilv welded by thevarious known industrial processes.

It is already known to make alloys endowed with characteristicsinteresting for their mechanical strength and corrosion resistance, saidallovs including nickel in a proportion of about 30 to and chromium in aproportion of about 23 to 27%. Such alloys have also a relatively lowcontent of carbon, manganese, silicon, phosphorus and sulphur.

The mechanical characteristics of these alloys when hot may be improvedby adding, in relatively important proportions, expensive alloyingelements such as tungsten and molybdenum. However, it could be recordedthat their addition generally decreased the weldability properties ofthe finished produce.

It is certain that, up to now, it was not possible to make an iron-basealloy capable of meeting all the hereinabove mentioned requirements, andin particular an alloy endowed with good mechanical strength, low creeprate, good resistance to corrosion, especially to the action of oxygen,as well as to the penetration of carbon into the alloy when it is infuel surroundings, good resistance to thermal shocks and hightemperature and reliable weldability properties.

The present invention aims at overcoming such drawbacks and diificultiesby creating a new alloy meeting all of the hereinabove mentionedrequirements, containing, besides iron, nickel, chromium, manganese,silicon and very little impurities, said alloy being remarkableespecially in that it contains a relatively low quantity of niobium.

According to another feature of the invention, the niobium contentranges substantially from 0.20% and 3.0% by weight.

According to still another feature of the invention, in the case wherethe alloy is intended to work at temperatures about 1200 C. to 1250 C.,the niobium content is of about 0.3 to 2.0% by weight.

According to still another feature of the invention and in an especiallyadvantageous method of execution, the niobium content is of about 1.20%by weight.

Extremely interesting qualities of the new alloy could be stated fromthe weldability point of view and confirming the corrosion resistance.

In a general way, the components of the alloy conformable to theinvention range within the following proportions:

Carbonfrom about 0.05% to 0.70% Chromiumfrom about 20% to 30% Nickelfromabout 30% to 40% Niobiumfrom about 0.20% to 3% Siliconfrom about 0.50%to 2.50% Manganesefrom about 0.50% to 2.50% Nitrogenfrom about 0.02% to0.20% Phosphous and sulphur-less than 0.05

the rest being iron.

As may be stated, the alloy is free from tungsten and molybdenum.Indeed, it has been noted that, on the one hand, they were relativelyexpensive alloying elements and, on the other hand, they decreasedrather than improved the qualities of the finished produce.

The hereinabove mentioned general composition permits to obtain verysatisfactory characteristics at high temperatures ranging from 800 C. to1200 C. However, it was stated that for more exacting conditions of use,for example between 1200 C. and 1250 C., in steady operation and forimportant lapses of time, the following more restricted compositionvalues should be observed:

Carbon-from about 0.10% to 0.60% Chromium-from about 23% to 28%Nickelfrom about 30% to 36% Niobiurnfrom about 0.3 to 2% Manganesefromabout 0.8% to 2% Siliconfrom about 0.8% to 2% Nitrogen-from about 0.02%to 0.2%

The rest being iron with the usual minimum impurities. It is preferredto use an alloy having the following composition:

Carbonabout 0.40%

Chromiumabout 26% Nickel-about 32% Niobium-about 1.2%

Manganeseabout 1.1%

Siliconabout 1.2%

Nitrogen-about 0.08%

The rest being iron and residual impurities, the latter kept as low aspossible in quantity.

It could be stated that, in some cases of use, a molybdenum content ofabout 0.5 to 1.5% improves some of the hereinabove mentioned propertiesof the new alloy. In contrast, in spite of the propitious action of theniobium, the proportions of the latter had to be limited. In whattungsten is concerned, its effects 'were not always profitable andindeed it could be either kept out or brought down to very low contentvalues.

In the following examples, selected from some practical tests, theimportance of the new alloy will be pointed out.

EXAMPLE 1 Three tests were effected at a temperature of about 950 C.during 1000 hours and 10,000 hours to evaluate the action of the niobiumon the properties of a hot base alloy including 33% of nickel and 25% ofchromium. Carbon, manganese, silicon, iron and impurities were 3 presentin the proportions corresponding to the hereabove indicated restrictedcomposition.

The tests were performed on an alloy free of niobium and then on asample wherein 1.26% of niobium has been introduced. The resultsobtained are indicated in Table I.

TABLE 1 Composition, Creep resistance until breaking percent at 950 inhectobar Ni Cr Nb R 1,000 h. R 10,000 11.

EXAMPLE 2 Still under the same operating conditions and with notmentioned alloying elements in quantities comparable to thosecharacterizing the invention, other comparative tests have been carriedout on a series of alloys to point out the action of elements such astungsten, molybdenum, niobium, alone or in combiation as precised inTable III.

TABLE III Breaking strength at Composition. percent 050 in hectobar NiCr Nb W Mo R 1,000 h. R 10,000 11.

It may be seen that Table III clearly points out the peculiarcharacteristics of the alloy conformable to this invention. The bestresults are obtained with a limited addition of niobium alone and theaddition of other alloying elements such as tungsten and molybdenum inthe absence of niobium results in lower creep characteristics whilestill constituting a more expensive alloy. Likewise, tungsten-niobiumand tungsten niobium molybdenum combinations do not present anytechnical or economical advantage.

Other creep tests to breaking under tension at higher temperatures (from1050 C. to 1200 C.) and for more extended periods of time have confirmedall points set in evidence by the 950 C. tests hereinabove indicated inTable III, and it was thus possible to be sure of the obvioussuperiority of the new alloy. Thus, for example, the comparative resultsaccording to the combinations indicated in Table III are reused in TableIV, wherein is indicated in hours the time of creeping to breaking for 2hectobar loads at a temperature of about 1050 C. and for 0.7 hectobarloads at a temperature of about 1200 C.

TABLE IV Compositions, percent Breaking time in hours T.: l,050 C.T.:1,200 Q. Ni Cr Nb W M0 2 hectobar load 0.7 hectobar The resistance tooxidation has been compared with that of a refractory alloy currentlyused for the whole of its qualities, containing especially 25% ofchromium and 20% of nickel, the other alloying elements being similar tothose given in the hereinabove mentioned restricted composition.

Measures taken at 950 C. and 10-50 C. after oxidation tests aresummarized in Table V, herebelow, in millimetres of thickness lost peryear.

Resistance to carburization has been checked by comparing the alloy ofthe invention with the same well known 25% chromium-20% nickel alloy.

Samples of each alloy have been cemented for 16 days and 32 days in asolid and carefully renewed cement.

Admixtures of carbon were carried out in each sample, on every mm. deepslice through more than 1 mm.

It could be observed that the richest layer was that located between 0.2and 0.3 mm. from the surface. The layer located between 1 and 1.1 mm.indicated the intensity of the deep carburizing, the intermediate pointsbeing substantially proportional.

The following table gives in percent the different carbon values, at thebeginning (0 day) of the cementation, 16 days later and 32 days later.It is thus easy to understand the advantages in corrosion resistanceoifered by this new alloy.

TABLE VI Maximum carbon content, 0.2 to 0.3 mm. deep layer Carboncontent in deep layer. depth: 1 to 1.1 mm.

Cementation time (in The invention also covers, by way of new industrialproducts, the produce obtained by means of the aforementioned alloy aswell as its various applications.

Of course, the invention is by no means limited to the method ofexecution and to the compositions indicated only by way of example. Inparticular, the invention covers all means constituting technicalequivalents to the described means as well as their combinations, if thelatter are carried out within the scope of the following claims.

What is claimed is:

1. Iron-base alloy for making high-temperature working slugs, usuable attemperatures as high as l2001250 C., containing carbon, nickel, chromiumand the minimum usual impurities, said alloy consisting essentially of:Carbonfrom about 0.10% to 0.60% by Weight Chromiurnfrom about 23% to 28%by weight Nickelfrorn about 30% to 36% by weight Niobiumfrom about 0.3%to 2% by weight Manganese-from about 0.8% to 2% by weight Siliconfromabout 0.8% to 2% by weight Nitrogen-from about 0.02% to 0.20% by weightReferences Cited the rest being iron and said usual impurities. UNITEDSTATES PATENTS 2. Iron-base alloy for making high-temperature workingslugs, usuable at temperatures as high as 1200-1250 C., 2121391 6/1938Amefss 75 128 N containing carbon, nickel, chromium, and the minimum 53381739 5/1968 a 75*128 R usual impurities, said alloy consistingessentially of: 2174025 9/1939 Wlse 75*1285 carbon about 040% b weight2,432,617 12/1947 Franks 75128 0 2,45l,547 10/1948 German 75-128 byWmght 3 306 736 2/1967 R d 11 75 12s 5 Nickelabout 32% by weight i un eNiobiumabout 1.20% by weight Manganese-about 1.10% by weightSiliconabout 1.20% by weight U S CL X R Nitr0genabout 0.08% by weight75128 -N 10 HYLAND BIZOT, Primary Examiner

